As per the standard cosmological model, galaxies are made through hierarchical assembly on cosmological timescales. Just like all other disk galaxies, our Milky Way galaxy also went through a violent merger of small galaxies in its initial years.
By the time of the collision, it was already forming stars, most of which are located within its thick disc, one of the two structures that come together to make up the Milky Way. The stellar remains of such events have been identified and it’s important to date them back to understand the evolution of the galaxy.
Due to lack of resources to obtain precise age of old stars. However, scientists from the University of Birmingham have managed to date some of the old stars in the Milky Way precisely. They achieved this feat by asteroseismology—the study of stellar oscillations—with kinematics and chemical abundances.
Old stars have similar age
After examining around 100 red giant stars, the team understood that some of these stars originally belonged to a satellite galaxy called Gaia-Enceladus that merged with our galaxy around 8-11 billion years ago.
The study findings showed that the surveyed stars have similar ages and are slightly younger than the majority of the stars that are believed to have formed within our galaxy.
“The chemical composition, location, and motion of the stars we can observe today in the Milky Way contain precious information about their origin. As we increase our knowledge of how and when these stars were formed, we can start to understand better how the merger of Gaia-Enceladus with the Milky Way affected the evolution of our Galaxy,” said Josefina Montalbán, lead author of the paper.
Combined data from different instruments
Scientists used data extracted from the Kepler satellite and merged it with the data taken from Gaia and APOGEE instruments. The information was implied on each star’s oscillation modes. Besides, the team also used spectroscopy that helped them calculate the chemical composition of the stars.
“We have shown the huge potential of asteroseismology in combination with spectroscopy to deliver precise, accurate relative ages for individual, very old, stars. Taken together, these measurements contribute to sharpen our view on the early years of our Galaxy and promise a bright future for Galactic archeoastronomy,” said Co-author, Professor Andrea Miglio.
